The present invention relates to an etching method of etching an oxide containing alkaline-earth metals as constituent elements, a chemical vapor growth apparatus for forming an oxide film containing alkaline-earth metals as constituent elements, and a cleaning method of the apparatus.
New materials that have not been conventionally used are beginning to be used in new semiconductor devices represented by very-large-scale semiconductor integrated circuits. So, chemical vapor deposition is beginning to be demanded to deposit thin films of these new materials. One of these new materials is barium strontium titanate ((Ba,Sr)TiO3):BST) which is a high-dielectric constant material used in a charge storage film (capacitive film) of a DRAM.
In the semiconductor device fabrication processes, dry etching superior in micro fabrication properties is widely used. However, alkali-earth metals such as Sr and Ba constructing the above material are not etched because the vapor pressure of a compound formed by a conventional etching gas is low.
Meanwhile, the semiconductor device fabrication processes extensively employ the formation of thin films by chemical vapor deposition (CVD) having high step coverage and capable of depositing in large areas. When a thin film is deposited by this CVD, a deposit sticks not only to a substrate for deposition but also to a reaction chamber exposed to a deposition gas or to jigs installed in the chamber. This deposit peels off owing to stress or mechanical stimulus, and the peeled dust particles fall on the substrate during deposition or during transfer of the substrate, thereby causing particle contamination of the formed thin film. Therefore, it is necessary to clean and remove the deposit, other than the objective deposit, sticking to the interior of the apparatus.
This cleaning method is desirably performed without disassembling the apparatus in order to raise the throughput. As this method of cleaning without disassembling the apparatus, a cleaning gas for changing the deposit into a substance having high vapor pressure is supplied into the apparatus to remove the deposit.
Unfortunately, alkaline-earth metals such as Sr and Ba constructing the aforementioned material cannot be removed because the vapor pressure of the compound formed by this conventional cleaning method is low.
A thin film containing alkaline-earth metals cannot be dry-etched and a chemical vapor deposition apparatus for depositing a thin film containing alkaline-earth metals cannot be cleaned with gas for the same reason: none of conventional etching gases and cleaning gases can form an alkaline-earth metal compound having high vapor pressure.
It is narrowly possible to etch a thin film containing alkaline-earth metals such as Ba and Sr by using chlorine trifluoride (ClF3) gas. However, a high temperature of 800xc2x0 C. or more is necessary for the etching, and yet the etching rate of Ba and Sr is lower than that of Ti.
Additionally, under severe conditions in which ClF3 is used at high temperatures, the corrosiveness of ClF3 increases. The most serious problem is that SiO2 is also etched when ClF3 is used at high temperatures. SiO2 is frequently used as interlayer dielectrics and a surface protective film in semiconductor devices. These SiO2-based films already formed are destroyed when a thin film containing alkaline-earth metals is dry-etched.
Also, a reaction chamber of a chemical vapor deposition apparatus is often made of quartz, and most jigs such as a substrate holder and a gas supply nozzle installed in the reaction chamber are made of quartz. Therefore, when a chemical vapor deposition apparatus for depositing a thin film containing alkaline-earth metals is cleaned by using a gas such as ClF3, quartz is eroded especially at high temperatures, resulting in destruction of the apparatus.
As described above, when a gas containing a halogen such as fluorine is used as an etching gas or a cleaning gas, no alkaline-earth metal compound having high vapor pressure is formed. Consequently, etching or cleaning takes a long time and hence is difficult to perform.
Also, when a fluorine-containing gas is used to etch or clean a chemical vapor growth apparatus, SiO2 is corroded, and this destroys an interlayer insulating film or the apparatus.
It is an object of the present invention to provide an etching method capable of easily etching an oxide of an alkaline-earth metal.
It is another object of the present invention to provide an etching method which does not etch SiO2-containing layers in a semiconductor device, or an etching method which etches a thin film containing an oxide film of an alkaline-earth metal without etching quartz members of a chemical vapor growth apparatus, and to provide a chemical vapor growth apparatus, and a cleaning method of the chemical vapor growth apparatus.
To achieve the above objects, an etching method of the present invention comprises the steps of preparing an oxide layer containing at least one type of alkaline-earth metal; and etching the oxide layer containing at least one type of alkaline-earth metal by using, as an etching gas, either a halogen gas other than fluorine gas, or a gas containing at least one material selected from the group consisting of an interhalogen compound consisting of halogen elements other than fluorine, and a halogen hydride consisting of a halogen element other than fluorine and hydrogen.
The step of etching the oxide layer desirably includes a step of etching in an ambient at not less than 500xc2x0 C.
The step of etching the oxide layer desirably includes a step of etching the oxide layer while changing an etching temperature.
The step of etching the oxide layer may includes:
a first etching step having a first etching condition; and
a second etching step having a second etching condition, and
the etching temperature in the first etching step is different from the etching temperature in the second etching step.
The second etching step is preferably successively performed after the first etching step, and the etching temperature in the first etching step is lower than the etching temperature in the second etching step.
The etching method may further comprise a step of repeating a plurality of times the step of successively performing the first and the second step.
The step of etching the oxide layer above-mentioned preferably includes a step of etching using chlorine gas as the etching gas.
The step of etching the oxide layer preferably includes a step of using a gas activated by plasma excitation as the etching gas.
The oxide layer above-mentioned is preferably a (Ba,Sr)TiO3 layer.
Chlorides, bromides, and iodides of alkaline-earth metals have relatively high vapor pressures. So, a thin film containing an alkaline-earth metal can be etched by using chlorine, bromine, or iodine. Also, since F highly corrosive for SiO2 is not contained, SiO2 portions used in a semiconductor device or in a film formation apparatus are not damaged. Therefore, dry etching using chlorine, bromine, and iodine gases can be effectively used as a cleaning means of a film formation apparatus. Additionally, the etching temperature can be lowered when active halogen radicals are formed by activating a halogen.
Particularly chlorides of alkaline-earth metals have relatively high vapor pressures, so alkaline-earth metals contained in a thin film can be etched at a high temperature of 700xc2x0 C. or more. However, in the temperature range of 700xc2x0 C. or more within which alkaline-earth metals can be etched, chlorides of metals such as titanium and tantalum evaporate and at the same time redeposit by thermal decomposition. This makes etching difficult to perform. A thin film containing a plurality of metals including alkaline-earth metals can be dry-etched by dividing the dry etching step into: a step of preferentially dry-etching metals whose chlorides thermally decompose to redeposit at high temperatures, and a step of preferentially dry-etching the alkaline-earth metals.
Also, by etching at a high temperature of about 800xc2x0 C. after etching is performed using chlorine gas at a low temperature of about 500xc2x0 C., metals other than alkaline-earth metals can be previously etched. This facilitates the etching at a high temperature of about 800xc2x0 C., since the residual film contains only oxides of the alkaline-earth metals.
In particular, metals such as titanium, tantalum, and ruthenium whose chlorides decompose and redeposit at a temperature of 700xc2x0 C. or more at which alkaline-earth metals can be etched are etched as fluorides in this temperature range by using an etching gas such as chlorine trifluoride. This makes two-stage etching feasible. Since etching of alkaline-earth metals and etching of metals other than the alkaline-earth metals can be performed at the same etching temperature, the etching can be performed within a short time period, and the etching gas consumption amount can be reduced. It is also possible to suppress film peeling caused by abrupt temperature changes during etching.
Furthermore, a thick film containing alkaline-earth metals can be etched by repeating an etching step of primarily etching alkaline-earth metals and an etching step of etching metals other than alkaline-earth metals. Since etching is done in stages, no perfect etching needs to be performed in the individual etching steps. This allows close temperatures such as 850xc2x0 C. and 700xc2x0 C. to be set as different etching temperatures. Accordingly, time loss resulting from etching temperature change can be reduced, and this shortens the etching time. By this shortening of the etching time, it is possible to suppress deterioration of an apparatus exposed to high-temperature exhaust gases and reduce the etching gas consumption amount.
Also, when etching is performed while the etching temperature is changed, a formed film containing alkaline-earth metals can be etched even in an apparatus having a reaction chamber whose etching temperature is difficult to abruptly change.
An etching method according to the second aspect of the present invention comprises the steps of preparing an oxide layer containing at least one type of alkaline-earth metal, and etching the oxide layer containing at least one type of alkaline-earth metal by using an etching gas composed of a gas containing a halogen element and a gas consisting of a halide of Ti.
The etching step desirably comprises the step of etching by using a gas containing at least fluorine as the gas containing a halogen element.
According to the second aspect of the present invention, even when Ti is selectively removed and no longer exists in an object to be cleaned, Ti is supplied from a gas. This produces halides such as Baxe2x80x94Ti and Srxe2x80x94Ti necessary to remove Ba and Sr. Consequently, perfect cleaning is possible.
Also, since halides of Ti have high vapor pressures, a gas amount containing Ti necessary for cleaning can be readily supplied. Additionally, since a halogen is also used as an etching gas, it does not interfere with etching.
A chemical vapor growth apparatus according to the third aspect of the present invention comprises a reaction chamber, a heating mechanism for heating the reaction chamber, a reaction gas supply unit connected to the reaction chamber to supply a reaction gas, a reaction gas exhaust unit connected to the reaction chamber to exhaust the reaction gas from the reaction chamber, and a member installed in the reaction chamber, wherein one of the reaction chamber and the member has a portion made of quartz, and at least a part of a surface of the quartz portion, which is exposed to the reaction gas, is coated with a fluoride of an alkaline-earth metal.
The portion of the quartz member, which is coated with a fluoride of an alkaline-earth metal is a portion to be exposed to a cleaning gas during cleaning of the apparatus.
Since fluorides of alkaline-earth metals have high resistance to a highly corrosive gas at high temperatures, damages to quartz members by a cleaning gas during cleaning can be suppressed.
Gas cleaning done by a CVD apparatus for a thin film containing alkaline-earth metals as constituent elements must be performed at high temperatures by using a highly corrosive gas. A protective film made from a fluoride of an alkaline-earth metal is particularly effective in cleaning.
Damages to quartz caused by a cleaning gas are especially remarkable when a cleaning gas containing fluorine is used. Hence, protection using a fluoride of an alkaline-earth metal is effective.
A cleaning method of a chemical vapor growth apparatus according to the fourth aspect of the present invention is a cleaning method of a hot wall type chemical vapor growth apparatus which uses a quartz member and deposits an oxide containing at least one type of alkaline-earth metal, comprising the steps of depositing a fluoride of an alkaline-earth metal at least on a surface of the quartz member, depositing the oxide on a substrate for deposition once or more, and etching the oxide by using an etching gas containing a fluorine compound.
The etching step desirably comprises the step of using a gas further containing a halide of Ti as the etching gas.
According to the fourth aspect of the present invention, a protective film is formed by using a gas as in normal CVD, so the apparatus need not be disassembled in the formation of the protective film. Since the protective film is formed, an etching gas containing, e.g., ClF3 can be used. Even when the protective film deteriorates by repeated BST film formation and ClF3 cleaning, the protective film can be re-formed without immediately disassembling the apparatus. This increases the availability and throughput of the apparatus.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.